Digital FM receiver for recovering FM digital data frame in mobile communication system

ABSTRACT

There is provided a digital data receiver for recovering at least one message word signal from a digital data frame. The digital receiver includes a digital FM demodulator for receiving frequency modulated signals, and for demodulating a dotting sequence signal, a word sync signal and a message word signal of each sub-frame which is in digital data frame, a dotting detector for detecting a dotting sequence signal of at least one sub-frame among the signals demodulated by the digital FM demodulator, based upon a predetermined signal which is shorter than the length of each dotting sequence signal of the each sub-frame, detecting means for determining the termination of receiving of the digital data frame after the dotting detector detects the dotting sequence signal, and for detecting a new digital data frame followed by the digital data frame; and a message processor means for recovering a message word signal in the digital signal frame which is related to the dotting sequence signal detected by the dotting detector. A method for recovering at least one message word signal from a digital data frame is also disclosed.

PRIORITY

This application claims priority to an application entitled “DIGITAL FMRECEIVER FOR RECOVERING FM DIGITAL FRAME IN MOBILE COMMUNICATION SYSTEM”filed with the Korea Industrial Property Office on Jun. 28, 2000, andassigned U.S. patent application Ser. No. 2000-35989, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an FM digital data receiverusing IS-95 dual mode in which the receiver is selectively operable ineither FM or code division multiple access (CDMA) in mobilecommunication systems. More particularly, the present invention, whencontinuously receiving a plurality of digital data frames in voicechannel mode, relates to an FM digital data receiver for receiving amessage without losing the message being repeated in said digital dataframe, and a method for receiving the message.

2. Description of the Related Art

Analog mobile communication systems, such as AMPS (Advanced Mobile PhoneService) system, are still being used broadly in the region of NorthAmerica. Meanwhile, the demand of digital mobile communication systemshas also been gradually expanding. In fact, several mobile telephoneoperators have been gradually changing their analog mobile communicationsystems to digital mobile communication systems, with the result thatsome users can not communicate in some areas because different modes ofcommunication are used. Therefore, there have been requests for a dualmode mobile phone being capable of communicating with both analog anddigital mobile communication systems. The manufacturers or suppliers ofmobile terminals have recently developed a dual-mode mobile telephone tomeet the demand of the mobile telephone operators.

In a conventional analog mobile communication system, the demodulationof received FM communication signals is routinely performed using analogprocessing techniques. However, methods which allow analog communicationsignals to be processed using digital signal processing techniques haverecently been developed. These techniques, such as quadrature detectionprocesses, have enabled analog mobile communication systems to transmitboth voice and character message data.

FIG. 1 is a block diagram showing the structure of a digital datareceiver for AMPS adapted for dual mode operation.

Referring to FIG. 1, digital data receiver 1 includes an antenna 10receiving I and Q channel information signals transmitted from a dualmode transmitter (not shown), and analog receiver 11 processing said Iand Q channel information signals received through the antenna 10.Baseband I and Q signals being processed in said analog receiver 11 areprovided to analog to digital converter (ADC) 12 through each outputline 18 and 19 of the receiver 11. Within the ADC 12, baseband I and Qsignals are digitized to form 8-bit in-phase (I) and 8-bitquadrature-phase (Q) samples. The 8-bit I and Q samples are input to I/QFM demodulator 13. Within the I/Q FM demodulator 13, baseband I and Qsignals are converted into demodulated frequency signals. Thedemodulated frequency signals are provided to both an audio decimationfilter 15, and to a data recovery unit 14, respectively.

After the demodulated frequency signals are filtered within said audiodecimation filter 15, the demodulated frequency signals are provided toa vocoder (not shown) for recovery of the received audio information.Contemporaneously, the data recovery unit 14 extracts symbolsynchronization and message word signals from the demodulated frequencysignals. These extracted signals are decoded by the data recovery unit14, and then provided to a microprocessor 17. The microprocessor 17displays the inputted message word signals on a display device (notshown).

FIG. 2 is a block diagram of the structure of a message synchronizationcircuit incorporated into the data recovery unit 14 in order tosynchronize the symbols. An exemplary example of a messagesynchronization circuit is set forth in Korean Patent Application Ser.No. 1999-003241, filed Jun. 25, 1997, which is assigned to the assigneeof this application and is incorporated by reference.

FIG. 3 illustrates the structure of a digital data frame fortransmitting data over a forward voice channel (hereinafter FVC) in anAMPS system.

Referring to FIG. 3, a digital data frame includes a total of elevensub-frames, and each sub-frame is divided into three signal parts. Thethree signal parts are known as a given dotting sequence signal, a givenword sync signal and a message word signal, respectively, wherein eachsignal part is represented by a plurality of symbols or bits.Especially, the dotting sequence signal of the first sub-frame in thedigital data frame comprises a longer signal than the dotting sequencesignal of the rest of the sub-frames. Namely, the dotting sequencesignal of the first sub-frame is composed of 101 symbols in which 1 and0 are repeated, while the dotting sequence signal of the rest of thesub-frames are composed of 37 symbols in which are repeated 1 and 0. Theword sync signal included in all the sub-frames in the digital dataframe is composed of 11 symbols, having the same pattern, such as11100010010. The message word signal following the dotting sequencesignal and word sync signal in each sub-frame of the digital data frameis composed of 40 symbols. The message word signal is generated by a BCH(Boss-Chaudhuri-Hocquenghem) code method, which is used to code datacomposed of 28 symbols. The message word signal included in eachsub-frame is the same. The dotting sequence signal and word sync signalin each sub-frame allows a mobile telephone to synchronize the messageword signal that is received continuously.

The structure of the digital data frame of FIG. 3 was adopted by the TIA(Telecommunication Industry Association) as a standard structure, andthe receiving technology for receiving the digital data frame isdescribed in U.S. Pat. No. 5,812,607, which was issued to James A.Hutchison et al. (“HUTCHISON '607”). However, the receiving technologydescribed in the '607 patent has been developed under the circumstancethat if the space of the received digital data frame is broad enough,and message word signal must be detected at the start time of thedigital data frame. Therefore, if the radio channel was in a badcondition, the provability of detecting of the message word signal woulddecrease. Furthermore, with the increased demand for transmission ofshort-message service lately, there have been problems in cases ofsending the short-message, which usually consists of 40 symbols, byusing only one digital data frame. Therefore, to solve these kinds ofproblems, several U.S. mobile operators, such as SPRINT, havealternatively used the method of transmitting continuously a pluralityof digital data frames. Namely, if a short-message has more than 40symbols, they are divided and allotted to a plurality of digital dataframes, and then transmitted continuously with the plurality of digitaldata frames. In the case of continuously transmitting a plurality ofdigital data frames, a mobile phone should successfully receive theplurality of digital data frames transmitted continuously. However, thereceiving technology of Hutchison '607 suffers the problems of notreceiving accurately the digital data frames because of its use of themethod described below with respect to FIG. 4.

Referring to FIG. 4, the receiving method of a digital data frame withrespect to Hutchison '607 is set forth. The digital data frametransmitted from the dual mode transmitter (not shown) is synchronizedin the symbol sync circuit and the synchronized symbols are recoveredwithin the data recovery unit 14 of FIG. 1. The synchronized andrecovered symbols in the data recovery unit 14 are provided to a dottingsignal detector (not shown), and the dotting signal detector detects adotting sequence signal from the received symbols. If a specific patternof signal, for example a dotting sequence signal composed of 32 symbolsin which 1 and 0 repeat, is detected by the dotting signal detector, acontrol unit (not shown) operates a timer for a predetermined time.Generally, the timer sets a time corresponding to the length of adigital data frame. Therefore, if the dotting sequence signal isdetected and the timer is working, message word registers (not shown) inthe data recovery unit 14 store each message word signal of eachsub-frame in the digital data frame related to the detection of thedotting sequence signal. If the timer expires, the message word signalsare demodulated, and the dotting signal detector repeats the detectionof the next received digital data frame.

FIG. 5 shows a problem in the case of using the method of the FIG. 4.

Referring to FIG. 5, there is shown the case in which a dotting sequencesignal is detected in the second sub-frame because the dotting signaldetector (not shown) in the data recovery unit 14 of FIG. 1 could notdetect the dotting sequence signal of the first sub-frame in a digitaldata frame due to sudden weakness of radio channel strength. In thiscase, the timer operates for the time corresponding to the length of thedigital data frame from the time when the dotting signal detectordetects the dotting sequence signal. Therefore, if a plurality ofdigital data frames are received continuously, the timer terminatesduring receiving of a digital data frame following the first digitaldata frame. In the above case, the digital receiver can not be notifiedwhen the receiving of the first digital data frame ends. The problemlies in that the digital receiver can not separate the first digitaldata frame from a next digital data frame that includes a differentmessage word signal. Therefore, even though the digital data receiverreceives a next digital data frame having a different message wordsignal, it determines to receive the same digital data framecontinuously so that the message word register stores a differentmessage word signal. As a result, it negatively influences therecovering of the message word signal, and may even prevent receivingnext digital data frames.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof and means for accurately detecting the start and end time of digitaldata frames continuously received by a digital data FM receiver todemodulate a received FM digital data signal in a mobile communicationsystem.

It is another object of the present invention to provide a means fordetermining the end of receiving of a first digital data frame, and ameans for detecting whether or not a next digital data frame is receivedafter the first digital data frame.

It is still another object of the present invention to provide a longdotting sequence signal means for detecting a signal which is shorterthan the dotting sequence signal of the first sub-frame in the receiveddigital data frame, and which is longer than each dotting sequencesignal of the rest of the sub-frames, in order to detect whether thenext digital data frame is received after the received first digitaldata frame.

It is still a further object of the present invention to provide a frameend counter for decreasing a value from a predetermined value wheneversymbols transmitted from a symbol sync circuit are received, and forresetting to a predetermined value when the predetermined value reacheszero or the word sync detecting means detects a word sync signal of asub-frame that is related to the detection of the dotting signalsequence signal, after the dotting signal detector detects the dottingsequence signal.

It is still another object of the present invention to provide, when thedotting signal detector detects a dotting sequence signal and word syncdetector detects a word sync signal, a message word block counter forcounting whenever message word signals of sub-frames are received, and amessage accumulator for storing a plurality of message word signals ofsub-frames included in the digital data frame which is related to thedetection of the dotting sequence signal.

It is still a further object of this invention to provide a method forimproving the receiving ability as recovering message word signals ofeach sub-frame in the digital data frame after the number of messageword signals are accumulated to the highest level. The maximum number ofmessage word signals to be received is 11 because the total sub-framesis 11.

According to an aspect of the present invention, there is provided adigital receiver for recovering at least one message word signal from adigital data frame. The digital receiver includes;

a dotting signal detector, which is provided symbols of said signalsdemodulated by said digital FM demodulator, for detecting a dottingsequence signal of at least one sub-frame by determining whether thesymbols corresponding to the dotting sequence signal are continuouslydetected more than a determined value that is shorter than the length ofeach dotting sequence;

a long dotting sequence signal detector, which is provided symbols ofsaid signals demodulated by said digital FM demodulator, for detecting along dotting sequence signal by determining whether symbolscorresponding to dotting sequence signal are continuously detected morethan a determined value that is longer than the dotting sequence signalof the other sub-frames, but shorter than the length of the dottingsequence signal of the first sub-frame of the digital data frame aftersaid dotting signal detector detects dotting sequence signal of at leastone sub-frame;

a word sync detector, which is provided symbols of said signals, fordetecting word sync signal of each sub-frame;

after detecting at least one said dotting sequence signal, frame endingcounter for determining the termination of receiving of the digital dataframe when a predetermined total is reached by increasing or decreasinga determined value if each symbol of the digital data frame is detected,and resetting to a predetermined value if the word sync signal isdetected before reaching to the predetermined total; and

after said dotting signal detector detects the dotting signal and saidword sync detector detects the word sync signal, a message processormeans including a message accumulator that detects and stores at leastone message word signal of the sub-frame from the demodulated signals,for recovering the message word signal from the stored the message wordsignals until receiving of the digital data frame is terminated.

The method for recovering at least one message word signal from adigital data frame, being the same signal comprising the steps of:

(a) storing at least one message word signal of the digital data frame;

(b) detecting the dotting sequence signal of the digital data frame, andthen counting the number of symbols whenever each symbol is inputted;

(c) recovering the message word signal from all of the stored messageword signals at a time of detection when symbols corresponding to thedotting sequence signal are continuously detected more than a determinedvalue that is longer than the dotting sequence signal of the othersub-frames, but shorter than the length of the dotting sequence signalof the first sub-frame of the digital data frame, and then returning tothe step (b);

(d) recovering the message word signal from all the detected messageword signals at a time of reaching when a counting value of the symbolsis reached a determined value, and returning to the step (b), andinitializing the counting value of the symbol if the word sync signal ofthe digital data frame is detected before reaching to the determinedvalue;

(e) if the word sync signal is detected, storing the message word signalassociated with the detection of the dotting sequence signal of thedigital data sub-frame, and increasing counting value of message wordblock by 1; and

(f) returning to the step (b) if the counting value is not reached tothe determined value, and after recovering the message word signal fromthe stored message word signals at the time of detection when thecounting value reaches the determined value, and then returning to thestep (b).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram of a digital FM receiver incorporated in adual mode digital communication;

FIG. 2 is a block diagram of a symbol sync circuit which is incorporatedin the digital FM receiver of FIG. 1;

FIG. 3 illustrates the structure of a digital data frame received by thedigital FM receiver of FIG. 1 during forward voice channel (FVC) mode;

FIG. 4 illustrates a digital data frame processed according to priormethods and received by the digital FM receiver during forward voicechannel (FVC) mode;

FIG. 5 is an example of showing the detection of the dotting sequencesignal delayed in a prior art processing digital data FM receiverreceived by the digital FM receiver during forward voice channel (FVC)mode;

FIG. 6 is an preferred embodiment of a digital FM receiver forprocessing digital data frames received continuously according to thepresent invention; and

FIG. 7 illustrates the steps for processing digital data frames receivedcontinuously in the digital FM receiver of FIG. 6 according to thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described indetail hereinbelow with reference to the accompanying drawings. In thefollowing description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. It willbe apparent, however, to one skilled in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known functions or constructions have not been describedso as not to obscure the present invention.

FIG. 6 is a block diagram illustrating a digital FM receiver having adata recovery means incorporated in the digital FM receiver according toa preferred embodiment of the present invention.

Referring to FIG. 6, the dotting sequence signal, word sync signal andmessage word signal of each sub-frame, consisting of a plurality ofsymbols in the digital data frame that are demodulated by I/Q FMdemodulator 13 of FIG. 1, are provided to a symbol sync circuit 601. Thesymbol sync circuit 601 recovers clock information from the demodulatedsignals, and synchronizes each symbol by using the recovered clockinformation. In addition, the symbol sync circuit 601 recovers the valueof the symbol to be received by accumulating a plurality of sampledsignals during the interval of a symbol. A detailed explanation on thisis described in previously mentioned Korean Patent Publication Ser. No.1999-3241.

At the time when symbols are synchronized and recovered by the symbolsync circuit 601, a processor 610 controls the operation of a switch613, which is closed. The processor 610 also can control the operationof each apparatus without switch 613. However, the preferred embodimentusing switch 613 will be explained below. The processor 610 alsocontrols the switch 611 to be closed to node 614, in order to detect adotting sequence signal as soon as the switch 613 is closed. The dottingsignal detector 602 connected to node 614 accumulates a predeterminednumber of symbols, for example up to 32, related to dotting sequencesignal that is provided through switch 613. If the accumulated 32symbols have a pattern of repeated “1s” and “0s”, corresponding to thecharacteristics of the dotting sequence signal, the dotting signaldetector determines whether the symbol pattern corresponds to a dottingsequence signal or not. If the accumulated symbols correspond to adotting sequence signal, the dotting signal detector informs theprocessor 610. Once dotting signal detector 602 connected to node 614detects a dotting sequence signal, the processor 610 closes switch 611to node 615. Node 615 is connected to a long dotting signal detector603, frame end counter 604 and word sync detector 605, respectively.Once the switch 611 is closed to the node 615 so that symbols areprovided to the long dotting signal detector 603, the long dottingsignal detector 603 accumulates the inputted symbols up to apredetermined number of symbols, for example 42. If the accumulated 42symbols have a symbol pattern of repeated “1s” and “0s”, the longdotting signal detector 603 determines whether the symbol patterncorresponds to a long dotting sequence signal or not. If the symbolpattern corresponds to the long dotting sequence signal, the longdotting signal detector 603 informs the processor 610. After beinginformed, the processor 610 directs the message word accumulator 607 torecover the message word signal from the total message word signalsstored by a time the accumulator 607 is informed. Since detection of thelong dotting sequence signal means that the subsequent or new digitaldata frame which follows the digital data frame is being received, themessage word signal should be recovered from the total of message wordsignals stored in the message word accumulator 607 at the time ofdetection of the long dotting sequence signal. The detection of thearrival of a new digital data frame is performed by long dottingsequence signal detector 603. However, the dotting sequence signaldetector 602 also may be able to detect the long dotting sequencesignal.

When the dotting signal detector 602 detects the dotting sequencesignal, the frame end counter 604 resets to a predetermined countervalue described hereafter. When the switch 611 closes to node 615, theframe end counter 604 decreases by 1 from the predetermined value aseach symbol is provided to the frame end counter 604. If the frame endcounter reaches zero, the frame end counter determines that thereception of the current digital data frame is terminated and informsthe processor 610. With the termination of the reception of the digitaldata frame, the processor 610 directs the message word accumulator 607to recover the message word signal from the total of message wordsignals stored by a time the digital data frame is terminated. Here, thepredetermined value is designated to a specific value, for example 312,that is smaller than the total number of bits (i.e. 1032) of the digitaldata frame. Once the switch 611 is closed to node 615 and symbols areprovided from symbol sync circuit 601, the word sync detector 605accumulates the inputted symbols up to a predetermined number such as11. The word sync detector 605 determines whether the inputted symbolpattern is a word sync signal or not. If the inputted 11 symbols have aspecific pattern (i.e. 11100011001), the word sync detector 605 informsthe processor 610. When the dotting signal detector 602 detects thedotting sequence signal, and the word sync detector 605 detects the wordsync signal, the processor 610 controls switch 611 to be closed to node616. Node 616 is connected to a message word block counter 606 and amessage word accumulator 607, respectively. Once the switch 611 isclosed to node 616 and symbols corresponding to a message word signalare provided from symbol sync circuit 601, the message word accumulator607 stores the inputted symbols up to a predetermined value such as 40.The message word block counter 606 also counts how many the message wordsignals are stored in the message word accumulator 607. That is, duringreceiving a digital data frame, the message word accumulator 607 cancheck how many sub-frames are received based upon the detection of themessage word signal included in every sub-frame. If the counting valueof the message word block counter 606 reaches a determined value, suchas 11 corresponding to the total number of sub-frames included in thedigital data frame, the message word signals stored in the message wordaccumulator 607 is recovered. In contrast to the prior art that recoversthe message word signal by accumulating fewer message word signals afterdetecting the word sync signal, the preferred embodiment of the presentinvention accumulates more message word signals so that correction ofthe recovered message is improved.

Therefore, this invention provides, while the digital data frames aretransmitted from a transceiver, a digital receiver for recovering atleast one message word signal from a digital data frame in a mobilecommunication system. To achieve this, the present invention includes aframe end counter 604 to determine the termination of receiving of thecurrent digital data frame, and a long dotting signal detector 603 todetermine whether or not a next digital data frame is received followingthe first received digital data frame. This invention further includes amessage word block counter 606 for counting the message word signals asmessage word signals of the sub-frames are received in a digital dataframe.

Once the message word block counter 606 stores 40 symbols, and themessage word accumulator 607 is increased by 1, the processor 610controls the switches 612 and 614 to be closed to a majority votingmeans 608. The symbols are recovered by the majority voting means 608and BCH decoder 609 and provided to the processor 610 for displaying themessage.

The method of recovering at least one message word signal from thedigital data frame will now be explained in detail according to apreferred embodiment of this invention. It is noted, as described above,that the digital data frame includes a plurality of serial sub-frames.Each sub-frame consists of three signals, i.e. a given dotting sequencesignal, a given word sync signal and a message word signal. Each signalis modulated by frequency in a mobile communication system and then istransmitted from the mobile communication system. In addition, thelength of the dotting sequence signal of the first sub-frame in saiddigital data frame is longer than that of the dotting sequence signalsof the other sub-frames. The word sync signal and the message wordsignal included in said each sub-frame have the same signal pattern andsame length.

FIG. 7 illustrates, when digital data frames transmitted from atransceiver are continuously received by the mobile terminal, the stepsof detecting the starting of receiving or the end of the digital dataframe, and the step of recovering at least one message word signal fromthe digital data frame.

Referring to FIG. 7, symbols transmitted from symbol sync circuit 601 ofFIG. 6 are synchronized and the value of the symbols are recovered insteps 701 and 704. That is, all sample values of symbols inputted fromthe I/Q FM demodulator are repeatedly synchronized and recovered insteps 701 and 704. If a symbol is synchronized and recovered, one of aselected step among steps 702, 705 and 712 is performed. The dottingsignal detector 602 of FIG. 6 operates to accumulate synchronized andrecovered symbols inputted from the symbol sync circuit 601, and detectsthe dotting sequence signal of at least one sub-frame from a pluralityof the sub-frames included in the digital data frame in step 702. If thedotting signal detector 602 detects at least one dotting sequence signalin a sub-frame based upon a predetermined signal which is shorter thanthe length of dotting sequence signal of the rest sub-frames, theprocessor 610 is informed in step 703. Once the dotting signal detector602 detects at least one dotting sequence signal, the switch 611 isclosed from node 614 to 615. The counter 604 of FIG. 6 counts the numberof symbols inputted from the symbol sync circuit 601, and at the sametime the long dotting signal detector 603 detects a long dottingsequence signal, which is shorter than the length of the dottingsequence signal of the first sub-frame in the digital data frame, and islonger than the length of the dotting sequence signal of the rest ofsub-frames in the digital data frame in step 705. If the long dottingsequence signal is not detected and the counting number of the frame endcounter 604 is not zero in step 705, the word sync detector 605 detectsa word sync signal in the sub-frame in step 706. Once the word synchsignal is detected in step 706, the word sync detector 605 informs theprocessor 610 in step 707. If either the long dotting sequence signal isdetected by the dotting signal detector 602 or the counting number offrame end counter 604 reaches zero, reception of a digital data frame isterminated. Additionally, if the counting number of message word blockcounter 606 reaches zero, an error message is generated to show thatthere has been an error during reception of the digital data frame instep 708.

If the message word block counter 606 is at zero, then no message wordsignals of the sub-frames in the digital data frame have been detected.The error message generated in step 708 is sent to the processor 610 instep 709. Once the long dotting sequence signal is detected by the longdotting signal detector 603 in the step 705 or the counting number ofboth the frame end counter 604 and message word block counter 606reaches zero, the message word signal stored in the message wordaccumulator 607 is provided to a majority voting means 608 and BCHdecoder 609 for creating a reconstructed word in steps 710 and 715. Thereconstructed message word signal in the step 710 and 715 is provided tothe processor 610 and displayed or output on a display means or by anearphone (not shown) in step 717.

Meanwhile, if the word sync signal is detected in step 706, the messageword signal of the sub-frame associated with the detection of thedotting sequence signal is stored, and the counting number of messageword block counter 606 is increased by “one” in step 712. If thecounting number of the message word block counter 606 reaches apredetermined value, for example 11 corresponding to the number ofsub-frames included the digital data frame, the message word signalstored in the message word accumulator 607 is processed in majorityvoting means 608 in step 714. In the case where the counting number ofmessage word block counter 606 does not reach a predetermined value instep 712, the next message word signal of the rest of the sub-frames inthe digital data frame associated with the detection of the dottingsequence signal may be stored the message word accumulator 607, and thecounting of the message word block counter 606 is increased by 1 in step713. If there is a BCH decoding error in step 715, the processor 610 isinformed, and the above steps are repeated beginning from the firststep.

The above description of the preferred embodiments is provided to enableany person skilled in the art to make or use the present invention.Various modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments. For example, the means for detectingthe dotting sequence signal, the counters and accumulator areaccomplished by the use of digital signal processing technology. Thus,the present invention is not intended to be limited to the embodimentsshown herein but is to be accorded the widest scope consistent with theprinciples and novel features disclosed herein.

1. A digital data receiver for recovering at least one message wordsignal included in a received digital data frame which consists of aplurality of sub-frames, each sub-frame including a given dottingsequence signal, a given word sync signal and a message word signal inwhich each signal is represented by a plurality of symbols and modulatedby frequency in a mobile communication system, wherein a dottingsequence signal of the first sub-frame is longer than dotting sequencesignals of the rest of the sub-frames, and the word sync signal andmessage word signal of each sub-frame consist of the same length andpattern, the digital data receiver comprising; a digital FM demodulatorfor receiving frequency modulated signals, and for demodulating adotting sequence signal, a word sync signal and a message word signal ofeach sub-frame included in said digital data frame; a dotting signaldetector, which is provided with symbols of said signals demodulated bysaid digital FM demodulator, for detecting a dotting sequence signal ofat least one sub-frame by determining whether the symbols correspondingto the dotting sequence signal are continuously detected more than aspecific value that is shorter than the length of each dotting sequencesignal; a word sync detector, which is provided with symbols of saiddemodulated signals, for detecting the word sync signal of eachsub-frame; a frame end counter for counting the symbols received anddetermining termination of the received digital data frame by increasingor decreasing a counting number whenever each of the symbols is detecteduntil the counting number reaches a predetermined number, and forresetting to a initial number if the word sync signal is detected priorto reaching the predetermined number; and a message processor meansincluding a message word accumulator that detects and stores at leastone message word signal of the sub-frame from the demodulated signals,for recovering the at least one message word signal from message wordsignals stored in said message word accumulator until receiving of thedigital data frame is terminated.
 2. The digital data frame receiver asrecited in claim 1, wherein the frame end counter determines terminationof the received digital data frame after the dotting signal detectordetects at least one dotting sequence signal.
 3. The digital datareceiver as recited in claim 1, wherein the message processor meansrecovers the message word signal after the dotting signal detectordetects at least one dotting sequence signal and the word sync detectordetects the word sync signal.
 4. The digital data receiver as recited inclaim 1, wherein said message processor means further comprises amessage word block counter for counting the number of detected messageword signals included in each sub-frame of the digital data frame fromthe demodulated signals, and for recovering a message word signal frommessage word signals stored in said message word signal accumulator whenthe number of the detected message word signals reaches a determinedvalue.
 5. The digital data receiver as recited in claim 1, furthercomprising a long dotting sequence signal detector, which is providedwith symbols of said signals demodulated by said digital FM demodulator,for detecting a long dotting sequence signal by determining whethersymbols corresponding to dotting sequence signal are continuouslydetected more than a determined value that is longer than the dottingsequence signal of the other sub-frames, but shorter than the length ofthe dotting sequence signal of the first sub-frame of the digital dataframe after said dotting signal detector detects the dotting sequencesignal of at least one sub-frame.
 6. The digital data receiver asrecited in claim 5, wherein said message processor means recovers theone message word signal from message word signals stored in said messageword accumulator until the long dotting sequence signal is detected bysaid long dotting sequence signal detector.
 7. The digital data receiveras recited in claim 6, wherein said message processing means furthercomprises a message word block counter to count the number of detectedmessage word signals of each sub-frame from the demodulated signals, andfor recovering a message word signal from message word signals stored insaid message word accumulator until the number of detected message wordsignals reaches a determined value.
 8. A digital data receiver forrecovering at least one message word signal included in a receiveddigital data frame which consists of a plurality of sub-frames, eachsub-frame including a given dotting sequence signal, a given word syncsignal and a message word signal in which each signal is represented bya plurality of symbols and modulated by frequency in a mobilecommunication system, wherein a dotting sequence signal of the firstsub-frame is longer than dotting sequence signals of the rest of thesub-frames, and the word sync signal and message word signal of eachsub-frame consist of the same length and pattern, the digital datareceiver comprising: a digital FM demodulator for receiving frequencymodulated signals, and for demodulating a dotting sequence signal, aword sync signal and a message word signal of each sub-frame included insaid digital data frame; a dotting signal detector, which is providedwith symbols of said signals demodulated by said digital FM demodulator,for detecting a dotting sequence signal by determining whether thesymbols corresponding to the dotting sequence signal are continuouslydetected more than a first specific value that is shorter than thelength of each dotting sequence signal, and detecting a first dottingsequence signal of a new digital data frame by determining whether thesymbols corresponding to the dotting sequence signal are continuouslydetected more than a second specific value that is longer than thedotting sequence signal of the other sub-frames, but shorter than thelength of the dotting sequence signal of the first sub-frame of thedigital data frame; a word sync detector, which is provided with symbolsof said demodulated signals, for detecting the word sync signal of eachsub-frame; a frame end counter for counting the symbols received whichincreases or decreases a counting number whenever each of the symbols isdetected after the dotting sequence signal detection, for determiningtermination of the received digital data frame when the counting numberreaches a predetermined number, and for resetting the counting number ifthe word sync signal is detected prior to reaching the predeterminednumber, and for determining termination of the received digital dataframe through a way that counting number increased or decreased bynumber whenever each symbol is detected after the dotting sequencesignal detection reaches a predetermined number, and for resetting thecounting number to a initial number if the word sync signal is detectedprior to reaching the predetermined number; and a message processormeans including a message word signal accumulator that detects andstores at least one message word signal of the sub-frame from thedemodulated signals, for recovering the at least one message word signalfrom message word signals stored in said message word signal accumulatoruntil receiving of the digital data frame is terminated or the firstdotting sequence signal of the new digital data frame is detected bysaid dotting signal detector.
 9. The digital data frame receiver asrecited in claim 8, wherein the frame end counter determines terminationof the received digital data frame after the dotting signal detectordetects at least one dotting sequence signal.
 10. The digital datareceiver as recited in claim 9, wherein the message processor meansrecovers the message word signal after the dotting signal detectordetects at least one dotting sequence signal and the word sync detectordetects the word sync signal.
 11. A digital data receiver for recoveringat least one message word signal included in a received digital dataframe which consists of a plurality of sub-frames, each sub-frameincluding a given dotting sequence signal, a given word sync signal anda message word signal in which each signal is represented by a pluralityof symbols and modulated by frequency in a mobile communication system,wherein a dotting sequence signal of the first sub-frame is longer thandotting sequence signals of the rest of the sub-frames, and the wordsync signal and message word signal of each sub-frame consist of thesame signal length and pattern, the digital data receiver comprising: adigital FM demodulator for receiving frequency modulated signals, andfor demodulating a dotting sequence signal, a word sync signal and amessage word signal of each sub-frame which is in said digital dataframe; a long dotting sequence signal detector for detecting a dottingsequence signal of a first sub-frame by determining whether symbolscorresponding to the dotting sequence signal are continuously detectedmore than a determined value that is longer than the dotting sequencesignal of the other sub-frames, but shorter than the length of thedotting sequence signal of the first sub-frame of the digital dataframe; a frame end counter for counting the symbols received anddetermining termination of the received digital data frame by increasingor decreasing a counting number whenever each of the symbols is detecteduntil the counting number reaches a predetermined number, and forresetting to an initial number if the word sync signal is detected priorto reaching the predetermined number; and a message processing meanshaving a message word accumulator that detects and stores the messageword signal of at least one sub-frame from the demodulated signals, andfor recovering the message word signal from the message word signalsstored in said message word accumulator after the long dotting sequencesignal is detected by said long dotting sequence signal detector. 12.The digital data receiver as recited in claim 11, wherein said messageprocessor means further comprises a message word block counter forcounting the number of detected message word signals of the digital dataframe from the demodulated signals, and for recovering a message wordsignal from message word signals stored in said message word signalaccumulator when the number of the detected message word signals reachesa determined value.
 13. A method for recovering at least one messageword signal included in a received digital data frame which consists ofa plurality of sub-frames, each sub-frame including a given dottingsequence signal, a given word sync signal and a message word signal inwhich each signal is represented by a plurality of symbols and modulatedby frequency in a mobile communication system, wherein a dottingsequence signal of the first sub-frame is longer than dotting sequencesignals of the rest of the sub-frames, and the word sync signal andmessage word signal of each sub-frame consist of the same signal lengthand pattern, comprising the steps of: (a) demodulating frequencymodulated signals after receiving said frequency modulated signals ofthe digital data frame, and synchronizing the symbols of the signal; (b)detecting the dotting sequence signal from the synchronized symbols; (c)counting the number of synchronized symbols whenever each symbol isinputted after detecting the dotting sequence signal and determining thetermination of receiving the digital data frame if the counted numberreaches a predetermined value; (d) in step (c), initializing thecounting number of synchronized symbol if a word sync signal is detectedprior to reaching the predetermined value; (e) storing the message wordsignal of the sub-frame associated with the detection of the dottingsequence when the word sync signal is detected, and returning to thestep (d); and (f) recovering the message word signal from the storedmessage word signals when determining the termination of receiving thedigital data frame.
 14. A method for recovering at least one messageword signal included in a receiving data frame which consist in aplurality of sub frames, each sub-frame including a given dottingsequence signal, a given word sync signal and a message word signal inwhich each signal is represented by a plurality of symbols and modulatedby frequency in a mobile communication system, wherein a dottingsequence signal of the first sub-frame is longer than dotting sequencesignals of the rest of the sub-frames, and the word sync signal andmessage word signal of each sub-frame consist of the same signal lengthand pattern, comprising the steps of: (a) demodulating the frequencymodulated signals, and synchronizing the symbols of the signals; (b)detecting the dotting sequence signal from the synchronizing symbols;(c) detecting the word sync signal after detecting the dotting sequencesignal; (d) detecting the storing the message word signal afterdetecting the word sync signal of the sub-frame; (e) counting totalsub-frames; (f) counting the stored message word signals; (g) returningto (b) if the number of stored message word signal does not reach thenumber of total sub-frames of the digital data frame and recovering themessage word signal from the stored message word signals when the numberof stored message word signals reach the number of total sub-frames ofthe digital data frame.
 15. A method for recovering at least one messageword signal included in a receiving digital data frame which consist ofa plurality of sub frames, each sub-frame including a given dottingsequence signal, a given word sync signal and a message word signal inwhich each signal is represented by a plurality of symbols and modulatedby frequency in a mobile communication system, wherein a dottingsequence signal of the first sub-frame is longer than dotting sequencesignals of the rest of the sub-frames, and the word sync signal andmessage word signal of each sub-frame consist of the same signal lengthand pattern, comprising the steps of: (a) storing at least one messageword signal of the digital data frame; (b) detecting the dottingsequence signal of the digital data frame, and then counting the numberof symbols whenever each symbol is inputted; (c) recovering the messageword signal from the stored message word signals when symbolscorresponding to the dotting sequence signal are continuously detectedmore than a first specific value that is longer than the dottingsequence signal of the other sub-frames, but shorter than the length ofthe dotting sequence signal of the first sub-frame of the digital dataframe, and then returning to the step (b); (d) recovering the messageword signal from all the detected message word signals when a countingnumber of the symbols reaches a second specific value, and returning tothe step (b), and initializing the counting number of the symbols if theword sync signal of the digital data frame is detected prior to reachingthe second specific value; (e) if the word sync signal is detected,storing the message word signal associated with the detection of thedotting sequence signal of the sub-frame, and increasing the countingnumber of a message word block by 1; and (f) returning to step (b) ifthe counting number of the message word block does not reach the secondspecific value, and after recovering the message word signal from thestored message word signals when the counting number of the message wordblock reaches the second specific value, and then returning to step (b).